1. Field of the Invention
The present invention relates in general to latch devices for latching the automotive pivotal back door at its fully closed position with an aid of electric power, and more particularly to power operated latch devices of a type which comprises a power operated latch proper mounted to either one of the back door and vehicle body and a striker secured to the other, so that when the back door is pivoted down to its incompletely closed position wherein a latch plate of the latch proper is half-engaged with the striker, the latch plate is drawn into a full-latch position with the aid of the electric power thereby to cause the back door to take a fully closed latched position.
2. Description of the Prior Art
One of the conventional power operated latch devices of the above-mentioned type is disclosed in Japanese Patent First Provisional Publication No. 62-244988. The latch device disclosed in this publication comprises a power operated latch proper mounted to the vehicle body and a striker secured to the pivotal back door. The latch proper generally includes a latch plate, a vertically extending threaded bolt, a nut member operatively engaged with the threaded bolt and carrying the latch plate and an electric motor for driving the threaded bolt to rotate about its axis. When the back door is pivoted down to its incompletely closed position causing a half engagement of the striker with the latch plate, the electric motor starts to run and thus rotates the threaded bolt about the axis in a direction to move the nut member downward therealong. Therefore, the back door is brought into its fully closed latched position.
However, in some of the power operated latch devices of the above-mentioned type, compact construction or size-reduction has been given little thought. In fact, when the latch device is applied to back doors of a type which needs a larger force for obtaining an assured seal between the back door in the closed latched position and the vehicle body, a high powered and thus large-sized electric motor is necessary, which usually causes a bulky or large-sized construction of the latch device.